There’s a lot of money in these SMR reactors and the first one was just had it’s design approved by the DoE which is one of the biggest hurdles. Prior to that the only real testing in the US could be done in national labs (like in the Idaho one).
I’m no expert, but from my understanding aside from the land being reused, nothing really from a former coal/natural gas plant could really be reused. The DOE regulations and requirements would require all infrastructure to be built for the reactors. The security requirements are also significantly more than a fossil fuel plant. However, the connections to the grid could be reused and upgraded and former plant personnel could be retrained. The biggest issue is cost unfortunately, the Vogel plant in Georgia has been like a decade behind schedule and significantly over budget. Part of that is due to how long we went from building plants in the 70s, to the nuclear scare to now building again. So much knowledge has been lost from crafts people who were experts in things like the specific types of welding needing, concrete mixtures etc. I think the future in the US at least will be the new prefabricated small scall reactors.
I think you’re confusing terminologies here. Nuclear is not renewable since it requires using a finite resource that has to be mined from the earth to create energy, however it is a nearly zero emission form of energy since it’s basically a giant tea kettle who’s steam spins a turbine to generate energy. That steam is just water vapor, the by products and spent fuel rods can be safely stored and processes or reprocessed. Wind, Solar, Geothermal and hydroelectric are renewable since they require no fuel to operate. All of the above could be considered green since they emit zero emissions unlike Coal and Liquid Natural Gas plants